1. Field of the Invention
The present invention is related to amplitude modulated carrier signals and more specifically to the demodulation of these signals.
2. Description of the Prior Art
The well-known process of using amplitude modulation to recover a baseband signal is the usual method utilized to recover modulated information such as gyroscopic output information. The demodulation of sensor signals can be extended to include quadrature detection demodulation so as to output the sine and cosine components as referenced to the case coordinate system of the sensor.
There are several prior art techniques available for performing in-phase and quadrature demodulation of an amplitude modulated double sideband suppressed carrier signal. The requirement exists, however, for an apparatus that not only addresses the need to demodulate a sinusoidal signal, but also the need to convert this demodulated signal into digital format. All of the prior art techniques, however, require analog circuitry to perform the demodulation process and then separately, the demodulated signal is digitized with an analog to digital converter.
Analog circuits are subject to many error sources including temperature sensitivity, noise, and induced error voltages from EMI. These error sources can be addressed in traditional ways, but in applications that have a small scale factor of the output signals, any additional noise presents major problems and such sources must be carefully scrutinized.
Temperature compensation can be performed to minimize temperature related errors such as bias drifts but any compensation requires knowledge of the system that is often acquired from empirical testing Such testing is time consuming and therefore expensive.
Noise encountered in analog circuits can generally be classified into a few specific categories such as Johnson noise, flicker or 1/f noise, shot (or Schottky) noise or popcorn noise. The error contribution of each type of noise must be studied and weighed to determine a correct method of reduction. This analysis adds cost and time delays to the final product.
The requirement still exists for an accurate yet inexpensive method for demodulation of a sinusoidal signal into in-phase and quadrature components digital data.